The present disclosure relates to electrostatic latent image developing toner.
According to electrophotography, in general, the surface of a photosensitive drum is electrostatically charged and is then subjected to exposure according to a to-be-formed image, thereby forming an electrostatic latent image on the surface of the photosensitive drum. Development of the formed electrostatic latent image with toner results in formation of a toner image. Further, the formed toner image is transferred to a recording medium, thereby obtaining a high quality image. Usually, toner particles (toner base particles) with an average particle diameter of 5 μm or larger and 10 μm or smaller are used as the tone used for formation of the toner image. The toner particles are obtainable in a manner that components, such as colorant, a charge control agent, a releasing agent, a magnetic material, etc. are mixed with a binder resin, such as thermoplastic resin, and the mixture is kneaded, crushed, and classified.
Further, in order to provide fluidity to the toner, to maintain the toner in an appropriate charge state, and to increase toner cleaning performance, inorganic fine powder of silica, titanium oxide, or the like is generally added as an external additive to the toner base particles.
The inorganic fine powder of silica, titanium oxide, and the like tends to be negatively charged in general. In particular, silica displays strong negative charge characteristics. In view of this, in the case using the inorganic fine powder for the positively charged toner, inorganic fine powder may be used which has a surface into which a positively charged polar group is introduced. As a toner to which such inorganic fine powder having a positively charged polar group is externally added, there is known a toner that contains silica treated with a silane coupling agent containing an amino group as an external additive.
Further, there is known a toner in which silica is externally added to the surfaces of toner base particles formed of a binder resin and colorant, wherein the silica includes silica A of which surface is treated with aminosilane and silica B of which surface is treated with a hydrophobizing agent.